In a portable, battery-powered device such as a cellular telephone, an external power input is usually provided so that the user can operate the device from a primary source of power such as house current or a vehicle's power source in order to conserve battery power. It is also desirable to have a battery charger internal to the device for recharging the unit's battery pack, which may be internal or external to the device. The device and its internal battery charger require a power supply or adapter external to the device to supply the proper voltage and current needed by the device to charge the internal battery or power the device.
Further, there are often a variety of external power supplies. For example, a high power version may be offered for fast charging the battery, while a low cost, low power version may be offered for slow charging the battery. Because the operation of the internal charger will differ depending on which external adapter is connected, the device must sense which type of external power adapter is present.
Accordingly, there is a need to provide a means for detecting the type of external power adapter which is connected to a device, and modify the operation of the apparatus as a function of the type of power adapter and battery. The invention leads to greater system flexibility and improved performance with all types of external power supplies.